The GST superfamily is a large group of proteins, the members of which are composed of two domains, an N-terminal thioredoxin-like domain (orange) that binds GSH, and a C-terminal all a-helical domain (blue), as illustrated by the structure of the GST protein from . coli in the figure to the right [1, 2). These proteins are found in most aerobic organisms. The GSTs were discovered in mammals over forty-five years ago [3]. For the first thirty years, their role in biology was thought to lie exclusively in the detoxification of endogenous and xenobiotic compounds by catalyzing the addition of GSH to electrophilic functional groups, as illustrated in Eq. 1. These reactions include electrophiles such as epoxides, enones and alkyl and aryl halides The catalytic diversity of GSTs also includes isomerization reactions, hydrolysis, and redox reactions with organic hydroperoxides, disulfides and, perhaps, selenides and selenates. The functional diversity of these proteins exceeds their catalytic promiscuity. In bacteria and eukaryotes, the proteins are involved in detoxication reactions, catabollsm, the regulation of transcription and translation, the conductance of ions across membranes, and (we are almost sure) thiol homeostasis and protein folding. Nine of the approximately 4,400 proteins encoded by the . coli genome encode GST homologs [2, 4). The consensus residues for the GST homologs found in E. coli are shown in space-filling representation in the structure above to highlight the fact that the highly conserved residues in GST family members are principally involved in the structural stability of the fold rather than the function of the protein. The principal role of the thioredoxin-like domain is to bind GSH or related ligands while the a-helical domain tends to specify more subtle aspects ofthe protein function. The proteins are typically dimers.